generate fixed number of rows in a table - sql-server

Question

Not able to word the question properly, so couldn't search what I want. All I need is a dummy table with a single column of say guids, which I use it for some other purposes. Without actually writing same insert .. newID() n times, wondering if there is an elegant solution.
Similar question would be how do I populate a blank table with a int column with say 1-n numbers.
Row1: 1
Row2: 2
.......
Row100:100

Answer 1

Instead of a recursive CTE, I recommend a set-based approach from any object you know already has more than 100 rows.
--INSERT dbo.newtable(ID, GUID)
SELECT TOP (100) ROW_NUMBER() OVER (ORDER BY [object_id]), NEWID()
FROM sys.all_columns ORDER BY [object_id];
For plenty of other ideas, see this series:
http://www.sqlperformance.com/generate-a-set-1
http://www.sqlperformance.com/generate-a-set-2
http://www.sqlperformance.com/generate-a-set-3

Answer 2

You can do it recursively.
For numbers, f.ex.:
WITH r AS (
SELECT 1 AS n
UNION ALL
SELECT n+1 FROM r WHERE n+1<=100
)
SELECT * FROM r

Answer 3

This method is blisteringly fast. If you need to generate a numbers table from nothing, it's probably the "best" means available.
WITH
t0(i) AS (SELECT 0 UNION ALL SELECT 0), -- 2 rows
t1(i) AS (SELECT 0 FROM t0 a, t0 b), -- 4 rows
t2(i) AS (SELECT 0 FROM t1 a, t1 b), -- 16 rows
t3(i) AS (SELECT 0 FROM t2 a, t2 b), -- 256 rows
--t4(i) AS (SELECT 0 FROM t3 a, t3 b), -- 65,536 rows
--t5(i) AS (SELECT 0 FROM t4 a, t4 b), -- 4,294,967,296 rows
n(i) AS (SELECT ROW_NUMBER() OVER(ORDER BY (SELECT 0)) FROM t3)
SELECT i FROM n WHERE i BETWEEN 1 AND 100
Regarding performance:
Using SQL Server 2022, on a Xeon box from 2016, with SET STATISTICS TIME ON to measure query time I got these numbers:
(With t4 and t5 commented-out), it generates 256 rows in "0ms".
(With t4 uncommented) it generates 65,536 rows in 53ms.
(With t5 uncommented in an INSERT FROM) it generated and inserted 4bn rows to a TABLE on-disk in about 65 minutes.
That's 66 million rows per minute, or about a million rows per second, nice!
Explanation:
The first CTE, t0 generates 2 rows.
Each subsequent CTE performs a CROSS JOIN of the previous CTE; a CROSS JOIN is a Cartesian Product which effectively squares the number of rows in each CTE step.
So having t0 through t3 means performing the Cartesian product three times, thus generating rows.
SELECT 0 FROM t0 a, t0 b is the same thing as SELECT 0 FROM t0 AS a CROSS JOIN t0 AS b.
Note that the results start at 1 and not 0 because ROW_NUMBER() starts at 1. To start at 0 do SELECT ( i - 1 ) FROM n in the outermost query.

Answer 4

One way;
;with guids( i, guid ) as
(
select 1 as i, newid()
union all
select i + 1, newid()
from guids
where i < 100
)
select guid from guids option (maxrecursion 100)

Answer 5

Just adding this as it wasn't listed:
A quick way to get 10 rows:
SELECT ROW_NUMBER() OVER(
ORDER BY N1.N)
, LOWER(NEWID())
FROM (VALUES(1), (1), (1), (1), (1), (1), (1), (1), (1), (1)) AS N1(N) -- 10
If you want it to be based on a variable:
DECLARE #N int = 10;
WITH Numbers(number)
AS (SELECT ROW_NUMBER() OVER(
ORDER BY N1.N)
FROM (VALUES(1), (1), (1), (1), (1), (1), (1), (1), (1), (1)) AS N1(N) -- 10
CROSS JOIN(VALUES(1), (1), (1), (1), (1), (1), (1), (1), (1), (1)) AS N2(N)-- 100
--CROSS JOIN (VALUES (1),(1),(1),(1),(1),(1),(1),(1),(1),(1)) AS N3 (N) -- 1,000
--CROSS JOIN (VALUES (1),(1),(1),(1),(1),(1),(1),(1),(1),(1)) AS N4 (N) -- 10,000
--CROSS JOIN (VALUES (1),(1),(1),(1),(1),(1),(1),(1),(1),(1)) AS N5 (N) -- 100,000
-- Etc....
)
SELECT *
, LOWER(NEWID())
FROM Numbers
WHERE number <= #N;